MONAGHAN, a county of Ireland in the province of Ulster, bounded east by Armagh, south-east by Louth, south by Meath, south-west by Cavan, west by Fermanagh, and north by Tyrone. Area 319,741 ac., or about 496 sq. miles. Pop. (1926) The north-western part is included in the great central plain of Ireland, but to the south and east the surface is irregular. The principal range is that of Slievebeagh, a barren tract extending into Fermanagh, its highest summit being 1,254 feet. The prin cipal rivers are the Finn, rising near the centre of the county and passing into Fermanagh, and the Blackwater, which forms the boundary with Tyrone. The Ulster canal passes the towns of Monaghan and Clones, affording communication between Lough Neagh and Lough Erne. In geological structure the county drops from the Upper Carboniferous outlier of Slievebeagh in the north-west to a Carboniferous Limestone area towards Monaghan town; but south of this a Silurian area stretches across the Cavan and Armagh borders. At Carrickmacross, an outlier of Car boniferous Limestone, Coal Measures (with poor seams of coal) and Trias is encountered. Gypsum has been quarried in the Trias, and lead ore was formerly mined in many places in the Silurian area. The Triassic clay furnishes excellent bricks. Eskers or glacial ridges occur at several places. Limestone is abundant, and worked at small cost. Freestone and slates are quarried.
The district now called the co. Monaghan was included in the district of Uriel or Orgial, known as Macmahon's country. It was made shire ground under its present name by Sir John Perrot in the reign of Elizabeth. At Clones there is a round tower, another at Inishkeen is in ruins. Near Clones are two large raths. There are several Danish forts. The 6th century abbey of Clones, once the seat of a bishopric, was rebuilt in the 14th century.
The soil is generally fertile where it rests on limestone, and there is also a mixed soil of deep clay, capable of high cultiva tion; but in the hilly regions a strong retentive clay prevails, which could be made productive only by careful draining and culture. Spade husbandry generally prevails. Oats, potatoes and turnips are the principal crops. The number of cattle, sheep, pigs, goats and poultry, is well maintained. Linen is the only manu facture of consequence, but the cultivation of flax has almost died out. The Belfast and Clones line of the Great Northern railway crosses the county from north-east to west, and the Dundalk and Clones line runs from south-east to west, with branches to Car rickmacross and to Cootehill (co. Cavan). Monaghan returns three members to Dail Eireann.